R2 Definitions

Question 1

Theoretical
yield

Answer 1

The maximum amount of product obtainable, assuming 100% of the limiting reactant is converted to product.

Question 2

Determining Limit Reactant

Answer 2

Divide amount by the molar ratio

Question 3

Rate of Reaction

Answer 3

Change in concentration of a particular reactant or product with time
In mol dm⁻³ s⁻¹

Question 4

Rate formula

Answer 4

Δ[product]/Δt or - Δ[reactant]/Δt (emphasis on the negative)

Question 5

Instantaneous Rate

Answer 5

Rate at t=0. Tangent at this point.

Question 6

Rates Measuring Techqniues

Answer 6

• Volume (needs to have gas particles)
• Mass (needs gas but doesnt work well with light gases which will not really change overall mass (e.g. hydrogen))
• pH (needs to be acid-base)
• Conductivity (needs to have ions)
• Change in transmission of light.
• Change in concentration (measured through titration)

Question 7

Gas method

Answer 7

2 ways:
1. Tube on the flask thats reacting with rubber stopper and this is connected to a plunger and displacement recorded.

2. Fill and invert a burette and under water have a tube coming from the reaction flask into the burette which fills it - only works with low-soluble gases

Question 8

Factors that impact rate

Answer 8

Concentration, temperature, surface area, and the presence of a catalyst

Question 9

Energy Profile Axis

Answer 9

x - reaction coordinate, y - potential energy.

Question 10

Energy Profile Steps

Answer 10

Reactants - EA - Transition state - drop - products.

Question 11

Catalyst

Answer 11

Increases the rate of a chemical reaction without itself undergoing chemical change. Most catalysts work by providing an alternative route for the reaction that has a lower activation energy. Equal change to forward and reverse reactions.

Question 12

Elementary Steps Molecularity

Answer 12

Unimolecular - An elementary step that involves a single reactant particle.

Bimolecular - An elementary step with two reactant particles. (e.g. NO + CO)

Termolecular - 3 but VERY UNLIKELY due to extremely low chance of 3 particles combining with sufficient E at the same time.

Question 13

Overall Reaction Order is equal to

Answer 13

Power of all reactants added together.

Question 14

How to determine order

Answer 14

Can only be determined experimentally through how concentration changes impact the rate.

Question 15

What cannot be in a rate equation

Answer 15

An intermediate - figure out the rate equation of what makes it.

Question 16

Can you prove a reaction mechanism from the formula?

Answer 16

No, you can only prove if it cannot be correct if the possible mechanisms fit the empirical findings - stoich and kinetic data match.

Question 17

Concentration-time graphs

Answer 17

Zero - y=-x
First - Negative exponential
Second - More harsh negative exponential

Question 18

Rate-concentration graph

Answer 18

Zero - Horizontal line
Second - y=x
Third - Positive exponential

Question 19

The two things the rate of a reaction is dependent on

Answer 19

1. Concentration of reactants (not all if some are zero-order).
2. k variable - can be changed by temperature changes/catalyst presence only.

Question 20

Arrhenius plot

Answer 20

In k = - (Ea)/(RT) + In A
This is a form of the equation for a straight line: y = mx + c
y axis - Ink
x axis - 1/T
Gradient - (-Ea)/(R)

Question 21

Formula to find Ea from the gradient

Answer 21

Ea (in J mol-1) = - gradient (in K) × 8.31 (R in J K-1 mol-1)

Question 22

Arrhenius Factor

Answer 22

The Arrhenius factor is a measure of the frequency of collisions and the orientation of reacting molecules. It represents the number of times reactants collide with the proper orientation to form products.

Question 23

Maxwell-Boltzmann Distribution Curves

Answer 23

Start at origin
y axis - Number of particles with a specific Kinetic Energy
x axis - Kinetic Energy

Question 24

5 things about equilibriums

Answer 24

1. They are dynamic - reactions still occur.
2. Only achieved in a closed
   system - no exchange of matter.
   3 The concentrations of reactants and products remain constant at
   equilibrium.
3. Macroscopic properties do not change as they depend
   on the concentrations
4. Equilibrium can be achieved from any start (e.g. all products or all reactants).

Question 25

Equilibrium Constant (K)

Answer 25

For aA + bB ⇌ cC+ dD K=([D]^c * [D]^d)/([A]^a * [B]^b)

Question 26

Reverse Reaction Equilibrium Constant

Answer 26

=1/K

Question 27

Le Chataliers Principle

Answer 27

A system at equilibrium when subjected to a change will respond in such a way as to minimise the effect of the change.

Question 27

How does concentration shift the equilibrium

Answer 27

Rate of the opposite reaction to whatever had its concentration increased will increase and a new equilibrium will be found further from the side which had concentration added. K does NOT change. On conc-time graph, when adding a specific reactant that reacant will have a sharp inc followed by a steady decrease (but new eq is higher than before) and other reactants will just decrease and be lower than before whilst products increase.

Question 27

Changes that shift the equilibrium list

Answer 27

- Concentration - Pressure (gas) - Temperature

Question 28

How does pressure shift the equilibrium.

Answer 28

If the number of molecules changes, then the equ shifts. An increase in pressure will favour the side with less molecules (determined by the molar ratio). E.g. CO + 2H₂ ⇌ CH₃OH has 3:1 particle ratio; therefore an increase in pressure will favour the forward reaction which will result in less molecules. K will not change.

Question 29

How does temperature shift the equilibrium.

Answer 29

- Temperature changes will shift K. - The equilibrium will shift to favour the direction that counter-acts the temperature change (inc of temp=shift to endothermic, decrease of temp=shift to exothermic)

Question 30

Exothermic

Answer 30

Reaction that releases energy (typically heat) into its surrounding, resulting in a negative ΔH.

Question 30

Endothermic

Answer 30

Reaction that absorbs energy (typically heat) into its system, resulting in a positive ΔH.

Question 31

How does a catalyst shift the equilibrium.

Answer 31

A catalyst decreases the activation energy for both the forward and reverse reactions equally, meaning both rates will increase to the same degree, maintaining the equilibrium and K.

Question 32

Reaction Quotient (Q) and what it allows you to do (in relation to K)

Answer 32

A measure of the relative amounts of products and reactants present during a reaction at a particular point in time where the reaction is not at equilibrium. Allows you to predict which way the reaction will proceed to reach equilibrium.

Question 33

ICE Method things to remember

Answer 33

- Use mols for ICE bit then convert to concentration - Balance equation and use mol ratios - If calculating concentrations from K and K is less than 10⁻³ then the x on reactants is removed. - Smallest x should be with co-efficient 1 and numbers with higher co-efficients in balanced will have higher x.

Question 34

ΔG and what its sign means for equilibrium

Answer 34

Negative - reaction proceeds in the forwards direction. Positive - reaction proceeds in the negative direction. 0 - reaction is at equilibrium

Question 35

ΔG and entropy at equilibrium

Answer 35

Gibs at minimum, entropy at maximum

Question 36

Homologous and Heterogenous Chemical Reactions

Answer 36

Homo - All in same physical state Hetero - Different physical states.